This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9902362-4 filed in Sweden on Jun. 21, 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to an electronic device having a proximity sensor, comprising: a loudspeaker for receiving an audio signal and having a loudspeaker coil with an impedance; a proximity sensor adapted to provide a control signal indicative of whether an object is in the proximity of the device.
This invention also relates to an electronic communications device having a proximity sensor comprising: communication means, and a proximity sensor adapted to provide a control signal indicative of whether an object is in the proximity of the device.
Moreover, this invention relates to a method of detecting proximity of an object relative to a loudspeaker with a loudspeaker coil which has an impedance.
2. Description of the Related Art
U.S. Pat. No. 4,613,830 discloses a proximity switch which includes an oscillation circuit whose oscillation output is variable depending on the inductance of a coil. An object in the proximity of the coil can be detected by observing a decline in the oscillation output. For the purpose of increasing the recovery speed of the oscillation which has dropped as a result of detecting a approaching object, a certain signal is applied to the oscillation circuit to increase its oscillation gain.
U.S. Pat. No. 5,337,535 discloses a capacitive proximity sensor for use e.g. in a telephone handset to sense whether an object e.g. a user, a table, or another object is in the proximity of the telephone handset. The disclosed proximity sensors include a sensing electrode mounted in parallel to a guard electrode; the electrodes are separated by an insulating layer. The sensing electrode and the guard electrode are driven in unison by an RF signal. The proximity of an object to the sensor is detected by monitoring the RF current flowing through the sensing electrode by means of a bridge coupling.
However, the above cited prior art requires unnecessarily many components for proximity detection, which reduce battery operating time and which require additional space in small-sized products (e.g. a mobile phone). Further, the manufacturing expenses and the risk of break-down of the product due to component failures are increased.
An object of the invention is therefore to reduce the number of components in small-sized products having proximity detection. It is a further object of the invention to increase battery operating time.
This is achieved when the electronic device mentioned in the opening paragraph is characterized by having oscillation means coupled to the loudspeaker coil and to provide the control signal in response to the impedance.
Consequently, the loudspeaker coil is used to sense proximity. When an object moves closer to the device (i.e. the loudspeaker coil), the object will tend to concentrate the magnetic flux density; and when the object moves farther away, it will separate the lines of flux cutting across the sensing element (i.e. the loudspeaker coil). The electromagnetic properties of the object are thus used to modulate the inductance of the loudspeaker coil used as a sensing element. Further, no additional components are needed for proximity detection, which in turn increases the reliability of the device while battery operating power may be conserved.
The prior art further involves the problem that when it is the purpose to decide whether an object is in the proximity of e.g. a mobile telephone, it is almost impossible to provide a well-defined proximity zone; and thereby almost impossible to decide when to execute a proximity triggered function. More specifically, a capacitive proximity sensor is very sensitive to varying electrical properties of possible objects and in particular sensitive to electronic charge (static charge) of possible objects. That is, even a change in humidity may result in an excessive change of the impedance of the capacitive element. Thus capacitive proximity sensors are very unreliable.
It is therefore another object of the invention to provide reliable decisions of whether an object is present or not.
This is achieved when the electronic communications device mentioned in the opening paragraph is characterized by having a proximity sensor coil with an impedance, and oscillation means coupled to the proximity sensor coil to provide the control signal in response to the impedance.
Consequently, it is possible to determine whether an object is present in the proximity of the coil in a way which is less sensitive to parameters uncontrollable in this respect such as humidity, static charge of the object, etc.